Cochlear implants have improved considerably over the course of the past 20 years, however, there is still a[unreadable] great deal of variability on all measures of post-implant performance. The general goal of the experiments[unreadable] proposed is to identify new ways to use electrophysiological measures to better understand the sources of[unreadable] that variability. Previous research from our laboratory has focused on measuring the response of the[unreadable] auditory nerve to electrical stimulation. The proposed studies will expand that early work to include not only[unreadable] measures of neural activity recorded from the auditory nerve but also cortically evoked responses recorded[unreadable] in the same individuals. These responses will then be compared with performance on a broad range of[unreadable] listening tasks including speech and music perception.[unreadable] While much of the research proposed will be conducted with adult implant users, the results will be directly[unreadable] applicable to pediatric populations. Peripheral measures such as the electrically evoked compound action[unreadable] potential (ECAP) recorded using telemetry systems incorporated into commercial cochlear implants have[unreadable] become important tools for both initial programming and monitoring of young children. It is not only possible[unreadable] to record the cortical responses we propose in young children but specific features of these responses have[unreadable] already been shown to follow developmental trends in children and to be indicative of performance (Sharma[unreadable] et al. 2002a; Ponton et al., 2000). The studies outlined in this proposal are important because they expand[unreadable] on previously published work to include assessment of cortical potentials evoked using a change in the[unreadable] pattern of ongoing electrical stimulation, a feature that simulates more closely the type of stimulation that is[unreadable] typical of everyday listening.[unreadable] Many of the proposed experiments focus on patients who use standard cochlear implants, however,[unreadable] experiments are also included that use these techniques in new populations of cochlear implant users such[unreadable] as those patients who use the Hybrid cochlear implant system and patients who receive bilateral cochlear[unreadable] implants. For each subject group, we have proposed experiments addressing the relationship between[unreadable] electrophysiological measures and performance. We will also assess changes that occur over time with[unreadable] continued implant use in both pediatric as well as geriatric populations. We expect that, based on results of[unreadable] the studies proposed, we will be able to more fully characterize the differences we observe across[unreadable] individuals and use that information to assist with clinical decision making, inform candidate selection and[unreadable] influence the ways the speech processor is programmed in order to maximize performance for an individual[unreadable] user.